1. Field of the Invention
The present invention relates to a developer containing device used in an image forming step for forming images by an electrophotographic method as well as an image forming apparatus having the developer containing device. The image forming apparatuses may include recording devices and display devices such as monochrome or color copiers, facsimiles, and others.
2. Description of the Related Art
The electrophotographic image forming apparatus includes a charging device for uniformly charging an image carrier corresponding to an image forming process, an image exposing device for forming an electrostatic latent image from electric charges on a surface of the image carrier, a developing device for visualizing the electrostatic latent image with a developer, a transferring device for electrically and mechanically transferring the visualized image on the image carrier onto a recording medium (paper or the like), a cleaning device for removing the developer (toner or the like) that remains on the image carrier after the transferring operation by the transfer device, and a fixing device for permanently fixing the visualized developer on the recording member by heat and pressure.
In the image forming apparatus having the above structure, process units are formed of the image carrier, the charging device, the exposing device, the developing device, the transferring device and the cleaning device. In general, the image forming apparatus employs a process unit in which the image carrier, the charging device, the cleaning device and the transferring device are integrated, although certain types of the image forming apparatuses do not employ such units.
In recent years, according to wide spreading of such apparatuses complying with the above processes and particularly the image forming apparatuses of which major features are full-color output, it has been required to reduce the sizes of the image forming apparatuses and to increase a print speed, and further to achieve a long life, high reliability, high image quality and low cost of the image forming apparatus.
For example, the developing device is provided with a developer containing device containing a developer. For preventing external leakage of the developer, the developer containing device has a sealing member (shaft sealing member or the like) arranged on a portion (e.g., a space between a rotation shaft for transporting developer and a bearing unit for the shaft) where a space is formed.
In the image forming apparatus, the transporting speed of the recording member has been increased for complying with a request to increase the print speed, and this generates a large amount of heat in the bearing unit. The developer is melted by heat generated in the bearing unit so that situations such as subsequent fixing of such developer to the sealing member will cause insufficient sealing by the sealing member, and fixing of the developer to the bearing unit will cause problems such as a failure in rotation of the rotation shaft. Japanese Laid-Open Patent Publication Nos. 2005-140968, 2000-019919 and 2003-057927 (Documents 1, 2 and 3, respectively) have pointed out the problems relating to defective image formation on the recording medium due to such failures, and have made various proposals for overcoming such problems.
The Document 1 has disclosed a developing device and an image forming apparatus. In this developing device, a rotation shaft for developer transportation has a hollow structure, and a fluid is supplied into the rotation shaft for cooling a bearing unit and thereby suppressing generation of heat in the bearing unit.
However, this structure additionally requires a pump for supplying the fluid into the developer transportation shaft as well as a heat exchanger for the fluid. This may increase sizes and a cost of the developing device. Further, the heat generated from the bearing unit is transferred to the fluid through the rotation shaft, and therefore may heat the developer to melt it before the heat is released to the fluid.
The Document 2 has disclosed a cleaning device and an image forming apparatus provided with the cleaning device. This device employs a heat-radiation shaft formed by extending a rotation shaft as well as heat-radiation fins arranged on the heat-radiation shaft. However, addition of the heat-radiation shaft and the heat-radiation fins may increase sizes of the apparatus. Further, the heat generated in the bearing unit is transmitted not only to the heat-radiation shaft but also to the rotation shaft (on the containing side of the developer) so that the rotation shaft may heat the developer to melt it.
The Document 3 has disclosed a developing device and a process cartridge provided with the developing device as well as an image forming apparatus. For this device, it has disclosed a structure in which a space having ventilation apertures for heat radiation is arranged at an end of the developing device, and a structure in which an air-flow assistance member is arranged in the above space. However, additional provision of the space having the ventilation apertures may increase sizes of the apparatus.